Establishment of a clinical SPECT/CT protocol for imaging of 161Tb

• Published in: EJNMMI physics 2020-07, Vol.7 (1), p.45-45, Article 45
• Main Authors: Marin, I., Rydèn, T., Van Essen, M., Svensson, J., Gracheva, N., Köster, U., Zeevaart, J. R., van der Meulen, N. P., Müller, C., Bernhardt, P.
• Format: Article
• Language: English
• Subjects: 161Tb; Algorithms; Applied and Technical Physics; Attenuation; Collimation; Collimators; Computational Mathematics and Numerical Analysis; Computed tomography; Computer simulation; Dosimeters; Emission analysis; Energy; Engineering; High resolution; Image quality; Image reconstruction; Image resolution; Imaging; Inserts; Lutetium isotopes; Medical imaging; Medicine; Medicine & Public Health; Noise sensitivity; Nonuniformity; Nuclear Medicine; Optimization; Original Research; Photons; Radiology; Recovery; Scattering; SPECT; Targeted radionuclide therapy; Tomography
• ISSN: 2197-7364; 2197-7364
• DOI: 10.1186/s40658-020-00314-x

Background It has been proposed, and preclinically demonstrated, that 161 Tb is a better alternative to 177 Lu for the treatment of small prostate cancer lesions due to its high emission of low-energy electrons. 161 Tb also emits photons suitable for single-photon emission computed tomography (SPECT) imaging. This study aims to establish a SPECT protocol for 161 Tb imaging in the clinic. Materials and methods Optimal settings using various γ-camera collimators and energy windows were explored by imaging a Jaszczak phantom, including hollow-sphere inserts, filled with 161 Tb. The collimators examined were extended low-energy general purpose (ELEGP), medium-energy general purpose (MEGP), and low-energy high resolution (LEHR), respectively. In addition, three ordered subset expectation maximization (OSEM) algorithms were investigated: attenuation-corrected OSEM (A-OSEM); attenuation and dual- or triple-energy window scatter-corrected OSEM (AS-OSEM); and attenuation, scatter, and collimator-detector response-corrected OSEM (ASC-OSEM), where the latter utilized Monte Carlo-based reconstruction. Uniformity corrections, using intrinsic and extrinsic correction maps, were also investigated. Image quality was assessed by estimated recovery coefficients (RC), noise, and signal-to-noise ratio (SNR). Sensitivity was determined using a circular flat phantom. Results The best RC and SNR were obtained at an energy window between 67.1 and 82.1 keV. Ring artifacts, caused by non-uniformity, were removed with extrinsic uniformity correction for the energy window between 67.1 and 82.1 keV, but not with intrinsic correction. Analyzing the lower energy window between 48.9 and 62.9 keV, the ring artifacts remained after uniformity corrections. The recovery was similar for the different collimators when using a specific OSEM reconstruction. Recovery and SNR were highest for ASC-OSEM, followed by AS-OSEM and A-OSEM. When using the optimized parameter setting, the resolution of 161 Tb was higher than for 177 Lu (8.4 ± 0.7 vs. 10.4 ± 0.6 mm, respectively). The sensitivities for 161 Tb and 177 Lu were 7.41 and 8.46 cps/MBq, respectively. Conclusion SPECT with high resolution is feasible with 161 Tb; however, extrinsic uniformity correction is recommended to avoid ring artifacts. The LEHR collimator was the best choice of the three tested to obtain a high-resolution image. Due to the complex emission spectrum of low-energy photons, window-based scatter correction had a minor impact o